1. Field of the Invention
The present invention relates generally to the photovoltaic generation of electrical energy. The present invention relates more particularly to photovoltaic roofing products for use in photovoltaically generating electrical energy.
2. Technical Background
The search for alternative sources of energy has been motivated by at least two factors. First, fossil fuels have become increasingly expensive due to increasing scarcity and unrest in areas rich in petroleum deposits. Second, there exists overwhelming concern about the effects of the combustion of fossil fuels on the environment due to factors such as air pollution (from NOx, hydrocarbons and ozone) and global warming (from CO2). In recent years, research and development attention has focused on harvesting energy from natural environmental sources such as wind, flowing water, and the sun. Of the three, the sun appears to be the most widely useful energy source across the continental United States; most locales get enough sunshine to make solar energy feasible.
Accordingly, there are now available components that convert light energy into electrical energy. Such “photovoltaic cells” are often made from semiconductor-type materials such as doped silicon in either single crystalline, polycrystalline, or amorphous form. The use of photovoltaic cells on roofs is becoming increasingly common, especially as system performance has improved. They can be used, for example, to provide at least a significant fraction of the electrical energy needed for a building's overall function; or they can be used to power one or more particular devices, such as exterior lighting systems and well pumps.
Accordingly, research and development attention has turned toward integrating photovoltaic cells with roofing products such as shingles, shakes or tiles. A plurality of photovoltaic roofing elements (i.e., including photovoltaic media integrated with a roofing product) can be installed together on a roof, and electrically interconnected to form a photovoltaic roofing system that provides both environmental protection and photovoltaic power generation.
Roofing products equipped with photovoltaic media often require electrical connectors to be attached to the products to allow electricity to be collected from photovoltaic cells and delivered to an electrical system. Such connectors can be, for example, mated connectors for connecting adjacent photovoltaic roofing elements, cables for connecting photovoltaic elements to the mated connectors, and/or junction boxes for interconnections within a single photovoltaic roofing element. The interface between such connectors can be susceptible to ingress of moisture. Even when the mated connectors are covered by overlying roofing elements, wind-driven moisture can work its way up the roof underneath the overlying roofing elements and into the connection.
Moreover, such devices must be robust to maintain the electrical connection in use and over time. In some cases, bulky connectors with safety locks may be required depending on the accessibility of the electrical connection. If the electrical connector will be covered by the roofing product in use, requirements can be less extreme, but a robust connection remains necessary. There exist low-profile connectors, but even these can be difficult to integrate with thin roofing products like asphalt or bituminous roofing shingles. For the case where the roofing product is thin or of low thickness, a low profile or flatter style of connector may be used. When such a low profile connector is used, useful connectors are often still quite bulky with respect to a thin roofing product such as, for example, an asphalt or bituminous roofing shingle equipped with photovoltaic media. Bulky connectors underlying the roofing product may telegraph their structure to the top surface of the shingle resulting in a wavy or distorted appearance that is undesirable. The local telegraphing of bumps over connectors can also lead to stress points and wear points on or in the roofing material and have deleterious effect on product performance. Other electrical elements, such as cables and junction boxes can also cause undesirable aesthetic appearance and stress/wear points. Moreover, electrical connectors can often be susceptible to ingress of water blown up the roof by wind, even when they are disposed beneath a shingle or other roofing element.
There remains a need for photovoltaic roofing products that address one or more of these deficiencies.